Burdick's T206 checklist - 521 in 1936?

[1880nonsports]

wagner/plank already included. Following the trail by looking through successive ACC catalogs might give a clue as to WHEN an accepted higher number was put to print - but as the cards are not listed individually no clues as to the actual cards not included in the count can be gleaned. I do have a run of ACC's albeit without any supplements but they are inaccessible at the moment.
Perhaps the WTI which would address the individual cards and also followed a pattern of being issued in skip numbered years would bear fruit. T206's are too new to light a fire under my ass to do the labor......Maybe some of the letters to follow will reveal such details and I imagine it was addressed in some of the newsletters published contemporaneous to such a discovery/addition. I haven't looked in Lew's "T" book in 20 years - maybe something in there or trader speaks? Maybe the Bulletin?
With all the heavy hitters here what's into dese damn cards - hard to believe there's no definitive answer yet.